1. Field of the Invention
The invention relates to a matrix type connector, and particularly to contacts used with a matrix type connector.
2. The Related Art
All personal computers require a CPU. To conveniently access the CPU for replacement and/or repair, a socket is generally provided to function as an intermediate device between a mother board and the CPU, wherein the socket is permanently mounted to the mother board while the CPU is detachably received within the socket.
A traditional socket is of a PGA (Pin Grid Array) type which includes a plurality of contacts in a matrix arrangement each having a pin type tail to be receivably soldered into a corresponding hole defined in the mother board, as disclosed in U.S. Pat. No. 5,489,218 which has the same assignee as the present invention. Such practice is implemented through a wave soldering process for mounting the socket onto the mother board, while recently SMT (Surface Mount Technology) has become a common method of assembly. Thus, an SMT process can be used to solder a BGA (Ball Grid Array) type connector to a mother board wherein each of a plurality of contacts of the socket in a matrix arrangement includes a solder ball attached to a lower tip thereof. Therefore, the BGA socket can be positioned on the mother board under the condition that the socket ball of each contact is seated on a corresponding paste on the mother board. The contact can then be fastened to the mother board by means of a combination of the solder ball and the corresponding paste through a reflow process.
The BGA arrangement for SMT is originally developed by IC chip packaging manufacturers. The material of the chip should be in compliance with that of the mother board to ensure that the solder joint between the solder ball and the paste will not break due to different CTEs (Coefficient of Thermal Expansion) between the mother board and the IC chip package during a high internal temperature operation of the computer.
Unfortunately, the connector is generally made by injection molding, thus, it is difficult to obtain a connector and a mother board with a similar CTE. Recently, the BGA type socket has been developed using BGA technology of the IC chip package, however, BGA sockets are not popular due to unreliability and a high defect ratio.
Therefore, an object of the present invention is to provide a contact arrangement for use with a matrix type connector adapted to be assembled to a mother board using an SMT process and having advantages of high reliability, low defect ratio and ease of assembly.